Resistance wire heaters of various configurations are well known in the prior art. One application of these types of heaters is in chemical analysis equipment, wherein an oven is needed to be able to closely control temperature of an oven space over an extended period of time. For example, the oven may receive test tubes that must be heated at a precise temperature over a set period of time.
One such heater is shown in FIGS. 1A-1C and designated by reference numeral 10. This heater is commonly referred to as a close quarter heater because of heater is typically confined in a location where space is at a premium. Thus, the heating elements of the heater have to be located in close proximity to the heater structure that this creates inherent problems in terms of the heater elements contacting heater structure and causing short circuiting. The heater of FIGS. 1A-C employs a cylindrical support 1 that has a plurality of insulators 3 mounted in spaced relationship along the inside of the support 1. The insulators each have a plurality of bores 5, along the length thereof and are secured to the support 1 using rivets 6. The bores are sized to receive the resistance wire while it is held by the insulators 3. Terminal block 9 is mounted to the support 1 to terminate the resistance wire.
As shown in FIG. 1B, the resistance wire 7 is in the form of a coil with two ends 11 and 13. The ends 11 and 13 are spirally threaded through the bores 5 in the insulators 3 until the resistance wire occupies all of the bores of the insulators 3. The ends 11 and 13 of the wire 7 are terminated using terminal block 9 for connection to a source of power via lead wires 15 and 17.
One problem with these types of close quarter heaters is that the resistance wire can migrate during heater operation. Based on a vertical orientation of the support 1 as shown in FIG. 1, this migration can occur both vertically so that the adjacent wires can touch each other and horizontally so that the wires can touch the support 1. In either event, this touching will result in a short circuiting and heater failure. As a result of migration, the prior art heater is equipped with insulation between the support and the resistance wire to avoid short circuiting.
Another problem with these types of heaters is that they are costly to make. The insulators 3 must be precisely formed and arranged on the support 1 so that the winding of the wire 7 can be performed. In addition and as mentioned above, insulation is required to separate the coiled wires extending between the insulators 3 and the support 1, thus increasing the cost of the heater. Typically, this is a mica sheet interposed between the support and the resistance wires.
In light of the problems with the prior art close quarter heaters, a need exists for an improved heater design that reduces or eliminates the short circuiting problem and provides a heater design that can be made in a more economical fashion.
The present invention responds to this need by providing a close quarter resistance heater that is economical to manufacture and does not have the short circuiting potential found in prior art heater designs.